External transformer will work well.
If you can find a mains to suitable multiple low voltage output windings transformer you can make your own step down. eg a 12/12/6 can be arranged as a 24:6 which is about right.
SMPS is a good idea due to efficiency.
Slightly more dangerous load safety wise - see below.
eg ye olde MC34063
This would cost a few dollars.
Note that with ANY non isolated circuit protection should be provided that will blow a fuse if the converter fails shirt circuit. Running yuour LCD on 24V would be a bad idea. See fig 24 in the above datasheet that shows an isolated output converter.
Resistor dropper + regulator Cheap and nasty solution that works OK
Note that this is quick and easy and nasty. Not recommended but doable.
Rectify 24VAC to about 34 Volts (!)
Pass this through a 47 ohm 20 Watt resistor (can be several smaller resistors in suitable series / parallel arrangement) and then
connect this to a 5V, 1A regulator such as LM340, 7805 etc.
Resistor max drop = 0.5A x 47R =~ 24 V.
V into regulator = 34-24 = 10V max.
Power in resistor = I^2 x R = 0.25 x 48 = 12 Watt.
Use much larger rating eg 20W+
You can tailor R so that V in to regulator is about 8V. Less may cause troubles.
You need a cap at regulator input.
Heatsink regulator appropriately.